1. Field of the Invention
This invention relates to distance measuring devices and, more particularly, to a wheeled distance measuring device with an associated counter that is actuated by a hit pin on the wheel as the wheel rolls along a surface on which a measurement is to be taken.
2. Background Art
Wheeled distance measuring devices are known in the art. It is conventional on such devices to rotatably mount a wheel on a frame that has an integral elongate handle to facilitate control thereof by an operator. The operator uses the handle to roll the wheel against a surface to be measured. As the wheel rotates, a hit pin engages a movable lever arm on a counter to pivot the lever arm and thereby record an increment of distance each time the hit pin moves against the lever arm. The counter has a visual display to indicate to the user the distance traversed by the wheel.
One typical counter mechanism has a lever arm which is pivotable between first and second positions and normally biased into the first position. As the wheel rotates, the hit pin engages the lever arm, effects movement of the lever arm from its first position to its second position, to thereby cause an incremental distance to be recorded on the counter, and then moves past the lever arm so that the lever arm is free to pivot under the bias force back to its first position.
It is important, for the above device to operate effectively, that the hit pin, upon each wheel revolution, engage and consistently move the lever arm from its first position to its second position. This requires that the hit pin be firmly implanted in the wheel. The wheels on such measuring devices are conventionally made from a deformable, high-friction, rubber material, which does not lend itself to the rigid attachment of hit pins. It is common with conventional structures for the hit pins, after repeated use, to become dislodged from the wheel. If the hit pin separates altogether from the wheel, the entire device is inoperable. If the hit pin becomes loose, it is possible that there may be sufficient play in the hit pin that it moves past the lever arm without effecting a required movement of the lever arm to record an increment of distance.
Typically, wheeled measuring devices are designed so that the wheel rotates in only one direction in use. Opposite rotation of the wheel causes the hit pin to jam against the lever arm in its first position until the wheel rotation is arrested. This jamming action can cause the hit pin to break off. This jamming action may also cause the opening through the wheel, which accepts the hit pin, to enlarge, thereby making it unusable for accepting a substitute hit pin.
It is also conventional to make the measuring wheels hollow with spaced annular side walls. Conventional hit pins have normally been directed through only one side wall. As a result, those in the art have contended with two vexatious problems: (1) that of the pin sliding lengthwise in and out of the opening through the side wall; and (2) that of the pin position varying due to the inherent flexibility of the annular wheel side wall.